1. Field of the Invention
The present invention relates to a safe medical-drug injector and, more particularly, to an automatically retractable safe medical-drug injector and a collapsible plunger combination thereof. The collapsible plunger enables the users of the injector to manipulate the injector by single-hand.
2. Description of the Related Art
It is well known that the major route of infection to the diseases such as Acquired Immune Deficiency Symptom (AIDS), hepatitis B or C is blood transportation. For the requirement to avoid the risk of such infection, an injector used by medical personnel or medicine taker is generally designed to be an unreusable or disposable syringe which can be used for only one time. However, most kinds of disposable syringes are not convenient to manipulate for that the user have to perform the injection by two hands. Accordingly, a diabetic may still choose to use the conventional injector instead of the disposable syringe to take insulin, and therefore the risk of getting infected with diseases through blood transportation still remains.
In view of this, a novel safe medical-drug injector which can be manipulated by single-hand is proposed and disclosed in Taiwan patent No. 520995 and U.S. Pat. No. 6,712,793. As shown in FIGS. 1A and 1B, the disclosed syringe includes a hollow barrel 12′, a needle hub 11′ for accommodating a needle 10′, an annular retracting spring 13′ and a breakable inward plunger 14′. The breakable inward plunger 14′ further includes a proximal part 17′, a breakable portion 18′ and a hollow distal part 19′ that are one-piece formed. When an injection is performed and completed, the user is able to break the breakable portion 18′ of the plunger 14′, which is inserted into the hollow barrel 12′, by further pressing on the plunger 14′ and cause the proximal part 17′ to draw into the hollow distal part while cause the needle hub 11′ and the used needle 10′ together to draw into the hollow barrel 12′.
As far as the plunger 14′ is concerned, the high symmetry and the high precision in making the breakable portion 18′ are required for the consideration of the operational convenience when the force is applied on the plunger 14′. Therefore, the manufacturing of the plunger 14′ is always costly due to the critical dimensional tolerance for the mold used to one-piece mold the plunger 14′. Besides, the break of the breakable portion 18′ and the retraction of the needle hub 11′ are not always achieved unless the direction of the applied force of the injection is limited to substantially parallel to the longitudinal axis of the plunger 14′. As a result, it is hard to perform an injection on the organ with larger curvature such as the back of neck, ear, eye, etc.